The following definitions are employed throughout the following discussion:
carrier setxe2x80x94a set of one or more frequencies associated with a PSD mask of a particular xDSL Recommendation;
downstreamxe2x80x94direction of transmission from the xTU-C to the xTU-R;
Galfxe2x80x94an octet having the value 816; i.e., the ones complement of an HDLC flag;
initiating signalxe2x80x94signal which initiates a startup procedure;
initiating stationxe2x80x94DTE, DCE and other associated terminal equipment which initiates a startup procedure;
messagexe2x80x94framed information conveyed via modulated transmission;
metallic local loopxe2x80x94communication channel 5, the metallic wires that form the local loop to the customer premise;
responding signalxe2x80x94signal sent in response to an initiating signal;
responding stationxe2x80x94station that responds to initiation of a communication transaction from the remote station;
sessionxe2x80x94active communications connection, measured from beginning to end, between computers or applications over a network;
signalxe2x80x94information conveyed via tone based transmission;
signaling familyxe2x80x94group of carrier sets which are integral multiples of a given carrier spacing frequency;
splitterxe2x80x94combination of a high pass filter and a low pass filter designed to split a metallic local loop into two bands of operation;
transactionxe2x80x94sequence of messages, ending with either a positive acknowledgment [ACK(1)], a negative acknowledgment (NAK), or a time-out;
terminalxe2x80x94station; and
upstream: The direction of transmission from the xTU-R to the xTU-C.
The following abbreviations are used throughout the following discussion:
ACKxe2x80x94Acknowledge Message;
ADSLxe2x80x94Asymmetric Digital Subscriber Line;
CDSLxe2x80x94Consumer Digital Subscriber Line;
DSLxe2x80x94Digital Subscriber Line;
FSKxe2x80x94Frequency Shift Keying;
HDSLxe2x80x94High bit rate Digital Subscriber Line;
HSTU-Cxe2x80x94handshaking portion of the xDSL central terminal unit (xTU-C);
HSTU-Rxe2x80x94handshaking portion of the xDSL remote terminal unit (xTU-R).
ITU-Txe2x80x94International Telecommunication Unionxe2x80x94Telecommunication Standardization Sector;
NAKxe2x80x94Negative Acknowledge Message;
POTSxe2x80x94Plain Old Telephone Service PSDxe2x80x94Power Spectral Density;
PSTNxe2x80x94Public Switched Telephone Network;
RADSLxe2x80x94Rate Adaptive DSL;
RTXxe2x80x94Request Retransmit;
VDSLxe2x80x94Very high speed Digital Subscriber Line;
XDSLxe2x80x94any of the various types of Digital Subscriber Lines (DSL);
xTU-Cxe2x80x94central terminal unit of an xDSL; and
xTU-Rxe2x80x94remote terminal unit of an xDSL.
1. Field of the Invention
The present invention is directed to a high speed communications device, such as, for example, but not limited to, a modem, a cable modem, an xDSL modem, a satellite communication system, a point-to-point wired, or a wireless communication system, that includes a handshaking or initializing protocol, and in particular, to an apparatus and method that provides error free communication by detecting errors and requesting the retransmission of errored communication messages.
2. Discussion of Background and Other Information
Recently, new communication methods are being proposed and/or developed to transmit data on a local twisted wire pair that uses a frequency spectrum above a traditional voice band (e.g., 4 kHz bandwidth). For example, various xe2x80x9cflavorsxe2x80x9d (variations) of digital subscriber line (DSL) modems have been/are being developed, such as, but not limited to, for example, DSL, ADSL, VDSL, HDSL, SHDSL and SDSL (the collection of which is generally referred to as xDSL). Each particular xDSL technology requires a robust start-up or initialization technique.
The ITU-T has published several recommended procedures for initiating a data communication, the following subject matter of which is expressly incorporated herein by reference in their entireties:
1) Recommendation V.8, entitled xe2x80x9cProcedures For Starting Sessions Of Data Transmission Over The General Switched Telephone Networkxe2x80x9d, published in September, 1994;
2) Recommendation V.8 bis, entitled xe2x80x9cProcedures For The Identification And Selection Of Common Modes Of Operation Between Data Circuit-Terminating Equipments (DCEs) And Between Data Terminal Equipments (DTEs) Over The General Switched Telephone Networkxe2x80x9d, published in August, 1996; and
3) Recommendation G.994.1, entitled xe2x80x9cHandshake Procedures For Digital Subscriber Line (DSL) Transceiversxe2x80x9d, published in June 1999. It is noted that this document is the final version of Temporary Document MA-006, that was published in March, 1999.
Documents (1) and (2), above, pertain to procedures for initiating a data communication over voice band channels. Document (3), above, pertains to initiating a data communication over xDSL channels.
Unfortunately, if a data reception error occurs in a message, even if the error is only a single bit in length, the data communication devices must completely restart, from the beginning, a handshake (initialization) procedure. Since initialization procedures often involve a plurality of messages or transactions, and thus, restarting a transmission from the beginning results in a significant loss of information and time. Thus, there is a need for an apparatus and method that minimizes an initialization recovery procedure, by retransmitting only the errored portion of a session instead of completely restarting the initialization procedure.
Accordingly, an object of the present invention is to develop a retransmission mechanism that retransmits an errored message that occurs during handshaking or initializing procedure. In a disclosed embodiment, the procedure is implemented as an extension to an xDSL handshaking and selection procedure (such as, but not limited to, for example, the above-noted ITU-T Recommendations G.994.1, V.8, and V.8 bis). According to the instant invention, if a communication device receives an errored message during a session, the communication device indicates the last correctly received message and requests a retransmission of the errored message. In addition, an optional feature of the present invention enables the retransmission request messages to suggest the length of a message frame to be used by a communication device in order to help reduce the occurrence of frames with errors.
According to an object of the invention, a communication device is disclosed that minimizes a retransmission of signals and messages when an errored message is received during a communication handshaking procedure. The communication device has a receiving section that receives signals from an initiating communication device, in order to detect when an errored message is received, and a retransmission request device that transmits, to the initiating communication device, a retransmission request message indicating that the errored message was received. The receiving section includes an error detecting device that operates to detect errored messages.
According to a feature of the invention, the retransmission request message may indicate which correct message was lastly received by the communication device. In addition, the retransmission request message can include information related to, for example, a suggested length of subsequent message frames to be transmitted, or a frame number of a multi-segmented message.
According to another object of the current invention, a method is disclosed for minimizing a retransmission of signals and messages when an errored message is received during a handshaking procedure of a communication session. According to this method, the handshaking procedure is monitored to determine whether a received signal contains an errored message. When the monitored handshake procedure determines that an errored message was received, a retransmission request message is transmitted to request retransmission of a portion of the handshaking procedure.
According to an advantage of the invention, data related to a Frame Check Sequence is examined to determine whether an errored message was received.
According to another advantage of the invention, the retransmission request message may, for example, indicate a last correctly received message, or, indicate a segment index number of a multi-segment message, or, record the type (or length) of the received message. In addition, a specific message type from a predetermined set of message types of the last correctly received message may be encoded with the retransmission request message.
According to a feature of the invention, the retransmission request message may indicate a suggested frame length of subsequently transmitted signals, which may be based, for example, on a frame length of a last correctly received message.
According to another feature of the invention, the communication session may be terminated when a predetermined number of errored messages (such as, for example, three) occur.
Another object of the invention concerns a method for minimizing a retransmission of signals and messages when an errored message is received during a handshaking procedure of a communication session, by monitoring received data related to a predetermined frame structure of a high speed handshaking procedure (such as, for example, data related to a Frame Check Sequence of an xDSL handshaking procedure), and transmitting a retransmission request message when the monitored predetermined frame structure indicates that the received data includes an errored message. In addition, the communication session can be terminated when a predetermined number of errored messages, such as, for example, three errored messages, are transmitted.
A still further object of the invention pertains to a method for minimizing a retransmission of signals and messages when an errored message is received during an xDSL negotiation procedure of a communication session. Received data related to a Frame Check Sequence is monitored. If the Frame Check Sequence indicates that the received data includes an errored message, a retransmission request message is transmitted. This message includes information identifying which correct message was lastly received. However, should a predetermined number of errored messages, such as three, occur, the communication session is terminated. In addition, the retransmission request message my contain information suggesting a frame length of subsequently transmitted signals. The suggested frame length may be based upon a frame length of the correct message that was lastly received.